This instructables is usefull if:
* you've got your arduino with atmega168 and you bought an atmega328 at you local electronics store. It doesn't have an arduino bootloader
* you want to make a project that doesn't use arduino - just a regular AVR chip (like the USBTinyISP) - you have a clean attiny2313/attiny48 etc that you want to burn firmware on.
Normally you would have to have an ISP (In System Programmer) like USBTinyISP to program your new chip. Having the arduino you can teach it to be a programmer thank to a great work done by Randall Bohn. He created Mega-ISP
- an arduino sketch that works like a programmer.